If you are looking at web development then it is good to have a basic understanding of CSS for general appearance and theming, or a more advanced knowledge of CSS for adding all the extra animations etc that are expected on a modern wizzo web site and/or mobile web UI.
When it comes to .Net (web) jobs, the demand seems to be largely around MVC and WCF. MVC is the top favorite web presentation framework and WCF seems to be the fav for web data services. A good knowledge of C# helps with both of these.
While I use mostly C# in my day job, I find Python appealing in many ways, and if it is something you enjoy using, there are often jobs advertised for experienced Python people.
Hi, There is very good resource that monitors programming language market share. Tiobe programming community index. http://www.tiobe.com/index.php/content/paperinfo/tpci/index.html It is not 100% accurate but allows to see overall trends in programming languages popularity.
But make good effort before final choose. Once you get professional, switching to another stack is not so easy. For example it's relatively easy to switch from PHP to Python or Ruby, but it is really hard to switch to Java or C (still completely possible, I know one very good PHP dev. who became Java architect in couple years).
It depends on the field one is working in and the platform stack used. At the enterprise level it is predominantly the Microsoft Platform stack, so C#, Asp.net, MVC, SQL Server, Exchange, SharePoint, Office, Azure etc.. Substitute C/C++ if the organisation is doing hardware/real-time.
In the mobile stack it will likely be Objective C (Apple) and whatever Android uses (with a bit of C# for windows phone, but the Microsoft Mobile platform is really built into their stack).
In the open source arena, I think it is still C/C++ for mainstream applications, PHP, Python, Apache and Linux for the platform development.
Software Engineer (the practice of real science, engineering and management)